Layers: remove duplication in LeechCoreFile

[eve-mem]

Super simple one.

I spotted some duplication of _chunk_size in the init for the leechcore layer.

        def __init__(self, leechcore_device):
            self._chunk_size = 0x1000000
            self._device = leechcore_device
            self._cursor = 0
            self._handle = None
            self._pad = True
            self._chunk_size = 0x1000000

This just removes one of the lines.

Thanks
🦊